Activating group

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In organic chemistry, an electron donating group (EDG) (electron releasing group (ERG) or activating group) is an atom or functional group that donates some of its electron density into a conjugated π system via resonance or inductive electron withdrawal, thus making the π system more nucleophilic. EDGs have the opposite effect on nucleophilicity as electron withdrawing groups (EWGs).[1][2] When attached to a benzene molecule, an electron donating group makes it more likely to participate in electrophilic substitution reactions. Benzene itself will normally undergo substitutions by electrophiles, but additional substituents can alter the reaction rate or products by electronically or sterically affecting the interaction of the two reactants.

Electron donating groups are generally ortho/para directors for electrophilic aromatic substitutions (though the electron withdrawing halogens are also ortho/para directors as they have lone pairs of electrons that are shared with the aromatic ring)

Electron donating groups are typically divided into three levels of activating ability. Electron withdrawing groups are assigned to similar groupings.

Strongly Activating Groups[edit]

  • -NH2
  • -NHR
  • -NR2
  • -OH
  • -O-

R = alkyl

Strongly activating substituents favor electrophilic substitution about the ortho and para positions.
This is illustrated by drawing the resonance structures of aniline: [1]

Moderately Activating Groups[edit]

  • -NHCOCH3
  • -NHCOR
  • -OCH3
  • -OR

Weakly Activating Groups[edit]

  • -CH3
  • -C2H5
  • -R
  • -C6H5

See also[edit]

References[edit]

  1. ^ "Electron donating group". Illustrated Glossary of Organic Chemistry. UCLA Department of Chemistry. Retrieved 16 November 2012. 
  2. ^ Hunt, Ian. "Substituent Effects". University of Calgary Department of Chemistry. Retrieved 16 November 2012.